Spark ignited (S.I.) Otto Cycle throttled internal combustion engines suffer from parasitic pumping losses associated with partial vacuums developed in their intake manifolds and in the cylinders above their pistons, as is illustrated in FIG. 1. This drawback is most prevalent when an Otto cycle engine is operated at part-load with the throttle partially closed. During each intake cycle of a throttled engine operating at part-load, extra work must be done by the piston as it draws the air-fuel mixture from the intake manifold into the volume expanding cylinder to counteract a force on the opposing face of the piston due to a pressure imbalance existing in the cylinder volume above the piston and in particular the crankcase volume below the piston. This extra work negatively affects the engine's specific fuel consumption and its level of anthropogenic emission and is the major drawback for vehicles requiring the use of larger displacement throttled engines in extended range operations and in engine applications requiring a wide flat responsive power curve.
To overcome these and other drawbacks, engine design has evolved away from the use of throttled internal combustion engines and towards the use of systems without throttle plates, which restrict incoming air supply, such as diesel and direct fuel injection engines, as illustrated in FIG. 2. However, direct fuel injection engines require sensitive components such as precise electronic fuel control systems, sensors, high pressure fuel pumps, and high pressure rapid fuel injectors that are costly and not inherently fail-safe. Likewise, diesel engines create high pressure combustion strains due to their inherent high compression and compressive shock generation which mandates a heavier, robust and costlier construction and further produce high levels of Nitrogen (NOx) emissions and dangerous cancerous particulates. Still, spark ignited prior art engines have only partially addressed the drawbacks related to pumping-loss by employing cylinder-on-demand engines, interconnecting cylinders for pressure equalizations by employing the natural pumping action of a reciprocating cylinder to displace air between cylinders, and by employing crankcase pumping systems for pumping fluid from the crankcase to ambient. However, such prior art systems do not fully eliminate throttled induced pumping-losses.
Also, prior turbo-compound engines used to recuperate energy from the exhaust gas by employing an exhaust gas flow turbine suitably coupled through a gearbox to the engine crankshaft are also known. However, such turbo-compound engines are not designed nor effective for part-load throttled engine operation and must primarily operate at high engine loads and employ high-ratio reduction gearbox couplings that add weight, complexity and cost to an engine.
What is therefore needed, and one object of the present invention, is a pneumatic coupling crankcase pressure reduction system and method so as to reduce the damaging parasitic effects of the differential pressure about a piston head during an intake cycle which is a source of part-load pumping-loss friction by providing an independent, supplemental, mechanical, fail-safe system comprising a turbo-compound engine variant for the pneumatic coupling of individual crankcase volumes that does not alter the cylinder charging integrity and stability.